The Caldwell Objects

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83 83 The Tweezers Galaxy NGC 4945 Type: Barred Spiral Galaxy (SBcd) Con: Centaurus RA: 13 h 05.4 m Dec: -49° 28' Mag: 8.8 Dim: 18.6' x 3.5' SB: 14.0 Dist: 17 million light-years Disc: James Dunlop, included in his 1827 catalog J. H ERSCHEL: Bright; very large; very much elongat- ed; very gradually a little brighter in the middle. Length much more than a diameter of the field, or than 15'. Its light extends to a star [of] 14th magnitude] beyond the parallel of Brisbane 4299. Position [angle] of elongation 38.7°. (h 3459) THE SKY IS FULL OF ILLUSIONS. FOR INSTANCE, on spring evenings we can see the Milky Way encircling us along the horizon, making us appear to be at the center of the galaxy; in reality we are well off-center but see several spiral arms meshed together into an apparent ring. Another common illusion relates to double stars. Not all double stars are pairs of physically related stars; the stars in some doubles are many light-years apart but happen to lie almost directly along the same line of sight. This same "coupling" phenomenon occurs with galaxies. Indeed, galaxies are master illusionists. Most curious are those bizarre, apparently disturbed galaxies whose photographs were collected in the 1960s by one of Edwin Hubble's students, Halton "Chip" Arp. Arp investigated relationships between these disturbed galax- 332 GC: Bright, very large, very much extended toward position angle 38.7°. NGC: Bright, very large, very much extended toward position angle 39°. ies and quasars found nearby. As Dennis Overbye shares in his Lonely Hearts of the Cosmos, Arp "turned out to be a genius at finding mystery. Every funny galaxy he inspected turned out to have a quasar tucked under an arm or at the end of a tendril of gas, or lines of them nearby. He photographed luminous bridges of gas that appeared to link galaxies whose redshifts projected them to be billions of light years apart." Arp also proposed physical relationships between several radio galaxies and other more "normal" galaxies that, in most astronomers' views, simply happen to lie in roughly the same direction on the sky. One of the more exotic and intriguing radio galaxies he collected was NGC 5128 (Caldwell 77), the peculiar radio galaxy Centaurus A. In 1968 Arp reported that one of Deep-Sky Companions: The Caldwell Objects
the two jets of radio-wave-emitting plasma streaming out of Centaurus A pointed right to our next target — the nearly edge-on barred spiral galaxy NGC 4945 (Caldwell 83). Although NGC 4945 is about 7½° due southwest of Centaurus A on the sky, the two belong to the Centaurus Group of galaxies and lie at similar distances from Earth. Does the radio jet connect the two galaxies? Maybe, maybe not. "Most astronomers dismissed Arp's diagrams and his computer-processed photographs as coincidences," Overbye writes. But the notion of "intergalactic pipelines" is not totally absurd, especially since HST has imaged a dark string of material flowing between two battered galaxies that bumped into each other about 100 million years ago. That pipeline begins in NGC 1410 and wraps around NGC 1409 like a ribbon around a package. Astronomers used HST to confirm that the 20,000-light-year-long pipeline is a continuous string of material linking these compact galaxies, and it probably was created during a tussle between them. In photographs NGC 4945 is a similarly 83 chaotic brew of stellar clumps and dusty patches seen through a scrim of foreground stars. The galaxy is quite large, spanning 77,000 light-years, and is receding from us at a speed of 560 km per second. It has the luminosity of 28 billion Suns and is the third-brightest galaxy in the IRAS Point Source Catalog (a list of objects whose brightnesses were measured at far-infrared wavelengths by the Infrared Astronomical Satellite). Most of the galaxy's infrared radiation comes from a compact region around the nucleus, which is surrounded by a dense, roughly 3 lightyear-wide torus of dust. Seyfert galaxies, like NGC 4945, are characterized by small, bright nuclei that emit intense and variable X-ray, infrared, and radio radiation while looking comparatively normal at visible wavelengths. Unlike the spectra of most spiral galaxies, which display a continuum and a few absorption lines, those of Seyferts are dominated by emission lines. These lines probably come from interstellar gas heated by X-rays streaming out of the galaxy's nucleus. There are two types of Seyfert galaxies. Type 2 Seyferts (like NGC 4945) have narrower emission lines than Type 1 Seyferts, indicating gas velocities of a few hundred km per second (or less) as opposed to thousands of km per second. The difference between the two Seyfert types is a consequence of the galaxy's apparent tilt. Type 1 emissions are associated with face-on galaxies, which allow us a clear view of the rapidly moving gas near the core. Since the cores of edge-on galaxies, like NGC 4945, are obscured by dust, we get to see only the narrower emission lines coming from slow-moving gas farther away from the center. Next to NGC 4151 in Canes Venatici, NGC 4945 is the brightest Type 2 Seyfert galaxy at high X-ray energies, leading astronomers to believe that its nuclear activity may be powered by a supermassive black hole. In a 2000 The Caldwell Objects 333
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DEEP-SKY COMPANIONS The Caldwell Ob
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DEEP-SKY COMPANIONS The Caldwell Ob
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Contents Foreword by Patrick Moore
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to be more difficult than others, s
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years of thought and observation ar
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XII position, type, angular size, a
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sky and share its splendors. There
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CHAPTER 1 About This Book O N ONE S
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times vog can back up and cause a s
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when there is moisture in the air.
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Herschel's original observations, p
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we use today and to one another? I
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SIMBAD (Set of identifications, Mea
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Caldwell 26. The objects in the Cal
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tion near the edges of the charts).
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nights of observing. Unless otherwi
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CHAPTER 2 The Caldwell Objects 1 1
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Because of its location far from th
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as strongly energized as would be e
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suggested by the patchiness of NGC
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4 NGC 7023 Type: Reflection Nebula
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astronomers found direct evidence o
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and his contemporaries. Why then wa
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6 Cat's Eye Nebula NGC 6543 Type: P
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Eighth-magnitude NGC 6543 is locate
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7 NGC 2403 Type: Mixed Spiral Galax
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according to theory, the gas densit
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8 Ghost’s Goblet NGC 559 Type: Op
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One other thing adds to the cluster
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RA: 22 h 56.8 m Dec: +62° 37' Mag:
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nebula is a near impossibility, eve
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1 0 The Horseshoe Cluster NGC 663 T
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heart of the cluster, dividing it i
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appears to be the edge of a rapidly
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1 2 NGC 6946 Type: Mixed Spiral Gal
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to the west by a row of similarly b
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the south-southwest. NGC 457, howev
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photographs. The cluster's bright "
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play begins at 8:00 p.m., when my e
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ightness by summing the contributio
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jewels. Here are sapphires, rubies,
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15 outer shell falls upon the retin
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"knots" have also been noted by exp
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tight gathering of a half-dozen rou
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1 7 NGC 147 Type: Elliptical Galaxy
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the center. A faint outer halo is a
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1 9 Cocoon Nebula IC 5146 (nebula)
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trickle into the pool surrounding t
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2 0 North America Nebula NGC 7000 T
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egion's size and mass extreme when
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The Caldwell Objects 20 87
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2 1 Box Galaxy NGC 4449 Type: Irreg
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fuse but obvious glow of patchy lig
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qualifier—the word "light" — ha
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with a sheen of light, especially a
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1003, NGC 1023, and NGC 1058 (a nic
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Way) that pop in and out of view as
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RA: 03 h 19 m 48 s Dec: +41° 30.7'
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Through the 4-inch, NGC 1275 is les
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(300,000 light-years), Pal 4 (360,0
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26 Silver Needle Galaxy NGC 4244 Ty
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2 7 Crescent Nebula NGC 6888 Type:
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Observatory, England) still lists a
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pie refractors and inefficient spec
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29 NGC 5005 Type: Mixed Spiral Gala
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s h a edges. r p However, Christian
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ulars; challenge yourself and your
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NGC 7331 is extended much farther t
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away" stars escaped the confines of
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sweep the telescope in a north-sout
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highly suspect by some. However, in
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33 Network Nebula; Bridal Veil Nebu
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A quarter-second later, the star en
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under the dark skies of Seagrave Ob
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35 NGC 4889 Type: Elliptical Galaxy
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magnitude 12.2 some 18' to the east
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36 NGC 4559 Type: Mixed Spiral Gala
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Comae Berenices, the obvious northe
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3 7 NGC 6885 Type: Open Cluster Con
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pressed, stars of magnitude 6 to 11
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of Herschel's telescope. W then e e
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see the dark needle near the third
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sion of a "thin flat ring of enormo
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(which does not appear on Sky Atlas
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not be found in planetary nebulae,
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star in a large naked-eye triangle
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4 0 NGC 3626 Type: Lenticular Galax
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40 NGC 4546 in Virgo, NGC 4138 in C
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Northern Hemisphere, and people cel
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magnitude field star 2' to the nort
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this state of affairs.) The Hyades
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4 2 NGC 7006 Type: Globular Cluster
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each square arcminute of its disk s
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4 3 Electric Arc NGC 7814 Type: Spi
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hook as my "train route." Start at
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230 billion Suns and a physical dia
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4 5 NGC 5248 Type: Mixed Spiral Gal
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of the field. Those living under da
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1" in a mere four days. Clearly, La
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porarily) even the most practiced o
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4 7 NGC 6934 Type: Globular Cluster
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stragglers are stars that appear to
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4 8 NGC 2775 Type: Spiral Galaxy (S
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with a CCD camera — discovered a
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this wreathlike network of dust and
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fuzzy patch of light with the unaid
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known as NGC 2244; and NGC 2239 sho
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At a glance the two stars at the cl
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On four plates taken with the Bruce
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years. A total of 43 star-cluster c
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5 2 NGC 4697 Type: Elliptical Galax
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northeast of the sixth star in the
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53 The Spindle NGC 3115 Type: Lenti
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and the 100-inch telescopes atop Mo
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emerge, followed by a diffuse outer
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perfection than is actually the cas
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jets, like a stream of water from t
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5 6 Pac-Man Nebula NGC246 Type: Pla
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the triple-alpha process, wherein t
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5 7 Barnard's Galaxy NGC 6822 Type:
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to show how the galaxy's western re
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core and limber arms, which, he wro
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esembles Jupiter . . . '" Smyth's f
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years" and suggests amateurs monito
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6 0 Ringtail Galaxy; Rataail Galaxy
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war. X-ray images taken by the Rosa
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W. Sinnott's NGC 2000.0 has a visua
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62 Milkweed Seed Galaxy NGC247 Type
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through the narrow haze. But give t
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was more readily seen in binoculars
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Society. Accepting that distance, w
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any large telescope that can provid
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ought it to our attention in the Fe
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inch the cluster shows a pyramid of
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NGC 253 is the brightest member of
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magnitude stars, one just to the ea
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6 6 NGC5694 Type: Globular Cluster
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you see its core dancing? Its starl
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cosmologist Halton Arp (Max-Planck
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and kinked. All this detail is wrap
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telescope. But seeing it takes more
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streamers begin to appear, but they
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tounding, because NGC 6302 is a mag
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70 Southern Pinwheel NGC300 Type: S
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would John Herschel suddenly fault
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Page 379 and 380: 9 2 Eta Carinae Nebula GC 3372 Type
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Page 399 and 400: 9 5 NGC 6025 Type: Open Cluster Con
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very wide double of near-equal inte
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went out and looked at the cluster
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NGC 2516 is 60 million years young
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and contains some 1,890 members, wh
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9 8 Coalsack Cluster NGC 4609 Type:
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it near the Swan? There is a still
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with the naked eye is a challenge.
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1 0 0 Lambda Centauri Cluster Colli
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position updates to (2000.0) R.A. 1
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Eta Carinae Nebula. But remember th
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9th magnitude. Of the latter, 23 ha
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103 1 0 3 Tarantula Nebula; True Lo
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southern-sky explorer Abbe Nicolas
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104 NGC 362 Type: Globular Cluster
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ters it has had thus far with the g
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ly east of NGC 362 we find the magn
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the eye ever inward and takes your
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1 0 5 Southern Butterfly NGC 4833 T
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stars"). Lacaille also likened NGC
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is about 7' in length, and nearly 2
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107 NGC 6101 Type: Globular Cluster
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evealed a significant blue-straggle
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ightest stars shine around 4th magn
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egion looks cold and disturbing, no
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The galaxy received some incidental
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This entry is obviously in error, b
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7 N G C 4 0 4 T y L p e n : G t a i
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pointed her 7x35 binoculars toward
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13 NGC 288 Type: Globular Cluster C
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your telescope on Eta Sculptoris an
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19 N G C 6 2 8 1 T y O p e C : n l
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C Name Type Con. R.A. Dec Mag. Size
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C Name Type Con. R.A. Dec Mag. Size
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Appendix B Why Messier Did N o t i
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A typical pattern for evening hunti
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Earth turns, the cluster would clim
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Initially Herschel made his living
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of the heavens with it. For his swe
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tube's front end. This meant that t
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Star in Collo Ceti" about the star
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years, Herschel would observe some
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fluid, but added that ages of obser
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Appendix D Photo Credits in order o
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A Abell426, 101 Acrux, 388, 392, 39
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index Caldwell 44, 173, 176-178 Cal
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and nebulae, 271, 274, 362 and open
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Hevelius, Johannes, 72, 81, 452 Hip
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M103, 49-50, 58-59 M110, 77 MACHOs.
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NGC 3324, 369 NGC 3372 (Caldwell 92
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Perseus Cluster, 101 Phi Cas Cluste
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Τ Tarantula Nebula (Caldwell 103),
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